1 About

This document summarizes updates to the analyses described in Wilson et al. 2025 including:

  • Updated spawner estimates, where available, through 2024 (file here. Previous estimates were through 2020.

  • Updated the ER time series base on the most recent estimates Will A. generated with the updated CWT indicator stock time series Ryan W. provided (file here)

  • Decomposed the Bella Coola spawner timeseries used in Wilson et al. 2025 (which ended in 2007) into separate time series for a handful of tribs that had decent temporal coverage including counts in recent decade (i.e., fish_creek, habensborg_slough, molly_walker, noohalk_ck, nookliklonnik_ck, snootli_ck, thorsen_ck)

  • Assumed all fish mature as 3 or 4 year olds by lumping the very tiny (<0.05%) assumed contribution of 5 year olds together with 4 year olds. This allows for a greater number of “complete” spawner-recruitment observations

  • Refit the AR-1 time varying model from Wilson et al. 2025 (JAGS model here) to the updated data described above.

  • Updated the regional productivity~sst relationships/fits.

  • Visualized population level estimates of spawner abundance over time to help shed light on observed trends in recent years.

These analyzes have not attempted to incorporate the StAD SIL (steam inspection log) review of data quality yet in part because to date is has been limited to only a half dozen systems and so seemed pointless to try and account for variation in observation error until we have more systems reviewed and with confidence ratings. With a more complete review of SILs for the systems considered in this analysis we can adapt the model to account for confidence in estimates (e.g., in likelihood by a assuming a large variance with the spawner observations that were are much less confident in).

Code to reproduce analysis, and this doc, can be found here.

Some preliminary, and non-exhaustive, insights based on these updated analyses include: 1. Total harvest rates have remained relatively consistent over the past 5 years, averaging ~30% in North to ~20% in south. Across all region harvest rates dipped in 2020 and have ticked slightly upward since.

  1. Estimates of intrinsic productivity rebounded slightly in the Hecate Lowlands region after reaching historical lows in the 2014-16 brood years, and averaged ~1.6 recruits per-spawner in the most recent brood years (2017-2020). These recent intrinsic productivities are associated with harvest rates expected to sustain maximum yield (\(U_{MSY}\)) of ~ 25%. In the other Central Coast regions intrinsic productivities have been variable by generally higher then in the Hecate Lowlands region. The high frequency variation in the Central Coast (South) region in recent years is suspicious and warrents further investigation.

  2. Summer SSTs declined by ~ 0.5 degrees in recent years compared to the highs seen in 2015-2019 during the marine heatwave years. However, summer SSTs since 2020 have still been higher than the long-term average (1980-present) Relationships between regional intrinsic productivities and SST in the summer of marine entry remained the same as previously estimated when the additional 4 years of data are included.

2 Reconstructed harvest rates

Reconstructed Alaskan and Canadian harvest rates across all fisheries by region. Estimates are based on CWT indicaotr stocks in Northern British Columbia and assumptions about vulnerability of Central Coast coho to fisheries in Alaska and Canada

Reconstructed Alaskan and Canadian harvest rates across all fisheries by region. Estimates are based on CWT indicaotr stocks in Northern British Columbia and assumptions about vulnerability of Central Coast coho to fisheries in Alaska and Canada

3 Coho populations

Coho populations origionally included in Wilson et al. 2025, by Management Area and Region. Populations from the Central Coast Regions were the focus of the updated analysis in this document

Coho populations origionally included in Wilson et al. 2025, by Management Area and Region. Populations from the Central Coast Regions were the focus of the updated analysis in this document

5 SST relationships

Sea surface temperatures (SSTs) in summer of coho ocean entry year by region and over time (a) and relationshiops between SST and regional intrinsic productivity by region (b).

Sea surface temperatures (SSTs) in summer of coho ocean entry year by region and over time (a) and relationshiops between SST and regional intrinsic productivity by region (b).

6 Returns by population over time

6.1 Hecate lowlands

6.2 Inner waters

6.3 Central Coast (South)

7 Spawners by population over time

7.1 Hecate lowlands

7.2 Inner waters

7.3 Central Coast (South)